Systems and methods for precise radio frequency localization using time difference of arrival

ABSTRACT

Systems and apparatuses for determining locations of wireless nodes in a network architecture are disclosed herein. In one example, an asynchronous system includes first and second wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture. The system also includes a wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first and second third wireless nodes in the wireless network architecture. The first wireless node transmits a communication to the second wireless node and the wireless node having an unknown location, receives a communication with an acknowledge packet from the wireless node, and determines time difference of arrival information between the first and second wireless nodes.

RELATED APPLICATIONS

This application is related to application Ser. No. 14/830,668, filed Aug. 19, 2015, entitled: SYSTEMS AND METHODS FOR DETERMINING LOCATIONS OF WIRELESS SENSOR NODES IN A TREE NETWORK ARCHITECTURE HAVING MESH-BASED FEATURES; and application Ser. No. 15/173,531, filed Jun. 3, 2016, entitled: SYSTEMS AND METHODS FOR PRECISE RADIO FREQUENCY LOCALIZATION IN THE PRESENCE OF MULTIPLE COMMUNICATION PATHS, which are both incorporated by reference herein.

FIELD

Embodiments of the invention pertain to systems and methods for precise radio frequency localization using time difference of arrival information.

BACKGROUND

In the consumer electronics and computer industries, wireless sensor networks have been studied for many years. In archetypal wireless sensor networks, one or more sensors are implemented in conjunction with a radio to enable wireless collection of data from one or more sensor nodes deployed within a network. Each sensor node may include one or more sensors, and will include a radio and a power source for powering the operation of the sensor node. Location detection of nodes in indoor wireless networks is useful and important in many applications.

Localization based on time difference of arrival (TDoA) technique for multilateration is performed using radio frequency measurements for determining location of wirelessly equipped objects in three dimensional space. RF-based localization may be performed in numerous ways. An exemplary implementation includes a hub and multiple sensor nodes. Note that the hub may be replaced with a node, or indeed, one or more of the nodes may be replaced with a hub. Distances are estimated using radio frequency techniques between all the individual pairs via RF communications. In TDoA, one node transmits a signal. Multiple other nodes receive the signal, and the time difference between reception at each receive node is calculated. TDoA requires synchronization of the receivers to accurately measure the difference in receive times. This can be done by operating all of the receivers on a shared clock and comparing absolute timestamps. In systems where a shared clock is not available, the receivers must be synchronized in another way.

SUMMARY

For one embodiment of the present invention, systems and apparatuses for determining locations of wireless sensor nodes in a network architecture are disclosed herein. In one example, an asynchronous system includes first and second wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture. The system also includes a wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first and second third wireless nodes in the wireless network architecture. The first wireless node transmits a communication to the second wireless node and the wireless node having an unknown location, receives a communication with an acknowledge packet from the wireless node, and determines time difference of arrival information between the first and second wireless nodes. In another example, a system for localization of nodes in a wireless network architecture includes first, second, and third wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture. The system also includes a fourth wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first, second, and third wireless nodes in the wireless network architecture. The one or more processing units of the first wireless node are configured to execute instructions to receive a communication with a forward packet from the fourth node, to transmit a communication to the second, third, and fourth wireless nodes in response to the forward packet, and to determine time difference of arrival information between the first and second wireless nodes and between the first and third wireless nodes.

Other features and advantages of embodiments of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which:

FIG. 1A shows an exemplar system of wireless nodes in accordance with one embodiment.

FIG. 1B shows an exemplar system of wireless nodes having multiple hubs for communicating in accordance with one embodiment.

FIG. 2A illustrates a system for localization of nodes utilizing time difference of arrival in accordance with one embodiment.

FIG. 2B illustrates an asynchronous system that is used for time of flight estimation in accordance with another embodiment.

FIG. 2C illustrates in one embodiment a 2-way ToF measurement system 1000.

FIG. 3 illustrates a timing diagram for communications of the system 200 in accordance with one embodiment.

FIG. 4 illustrates a system for localization of nodes utilizing time difference of arrival in accordance with an alternative embodiment.

FIG. 5 illustrates a timing diagram for communications of the system 400 in accordance with one embodiment.

FIG. 6 illustrates a method for determining location estimation of nodes using time difference of arrival techniques in accordance with one embodiment.

FIG. 7A shows an exemplary embodiment of a hub implemented as an overlay 1500 for an electrical power outlet in accordance with one embodiment.

FIG. 7B shows an exemplary embodiment of an exploded view of a block diagram of a hub implemented as an overlay for an electrical power outlet in accordance with one embodiment.

FIG. 8A shows an exemplary embodiment of a hub implemented as a card for deployment in a computer system, appliance, or communication hub in accordance with one embodiment.

FIG. 8B shows an exemplary embodiment of a block diagram of a hub 964 implemented as a card for deployment in a computer system, appliance, or communication hub in accordance with one embodiment.

FIG. 8C shows an exemplary embodiment of a hub implemented within an appliance (e.g., smart washing machine, smart refrigerator, smart thermostat, other smart appliances, etc.) in accordance with one embodiment.

FIG. 8D shows an exemplary embodiment of an exploded view of a block diagram of a hub 1684 implemented within an appliance (e.g., smart washing machine, smart refrigerator, smart thermostat, other smart appliances, etc.) in accordance with one embodiment.

FIG. 9 illustrates a block diagram of a sensor node in accordance with one embodiment.

FIG. 10 illustrates a block diagram of a system or appliance 1800 having a hub in accordance with one embodiment.

DETAILED DESCRIPTION

Systems and methods for precise radio frequency localization using time difference of arrival information are disclosed herein. In one example, an asynchronous system for localization of nodes in a wireless network architecture includes first, second, and third wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture. The system also includes a fourth wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first, second, and third wireless nodes in the wireless network architecture. The first wireless node transmits a communication to the second, third, and fourth wireless nodes, receives a communication with an acknowledgement packet from the fourth wireless node, and determines time difference of arrival information between the first and second wireless nodes and between the first and third wireless nodes.

In one example, the one or more processing units of the first wireless node are configured to execute instructions for a multilateration algorithm to determine a location of the fourth wireless node using the time difference of arrival information.

In various applications of wireless sensor networks, it may be desirable to determine the location of sensor nodes within the network. For example, such information may be used to estimate the relative position of sensors such as security cameras, motion sensors, temperature sensors, and other such sensors as would be apparent to one of skill in the art. This information may then be used to produce augmented information such as maps of temperature, motion paths, and multi-view image captures. Therefore, localization systems and methods are desired to enable accurate, low-power, and context-aware localization of nodes in wireless networks, particularly in indoor environments. For the purpose of this, indoor environments are also assumed to include near-indoor environments such as in the region around building and other structures, where similar issues (e.g., presence of nearby walls, etc.) may be present.

A wireless sensor network is described for use in an indoor environment including homes, apartments, office and commercial buildings, and nearby exterior locations such as parking lots, walkways, and gardens. The wireless sensor network may also be used in any type of building, structure, enclosure, vehicle, boat, etc. having a power source. The sensor system provides good battery life for sensor nodes while maintaining long communication distances.

Embodiments of the invention provide systems, apparatuses, and methods for localization detection in indoor environments. U.S. patent application Ser. No. 14/830,668 filed on Aug. 19, 2015, which is incorporated by reference herein, discloses techniques for RF-based localization. Specifically, the systems, apparatuses, and methods implement localization in a wireless sensor network that primarily uses a tree network structure for communication with periodic mesh-based features for path length estimation when localization is needed. The wireless sensor network has improved accuracy of localization while simultaneously providing good quality of indoor communication by using high-frequencies for localization and lower frequencies for communication.

Tree-like wireless sensor networks are attractive for many applications due to their reduced power requirements associated with the radio signal reception functionality. An exemplar tree-like network architecture has been described in U.S. patent application Ser. No. 14/607,045 filed on Jan. 29, 2015, U.S. patent application Ser. No. 14/607,047 filed on Jan. 29, 2015, U.S. patent application Ser. No. 14/607,048 filed on Jan. 29, 2015, and U.S. patent application Ser. No. 14/607,050 filed on Jan. 29, 2015, which are incorporated by reference in entirety herein.

Another type of wireless network that is often used is a mesh network. In this network, communication occurs between one or more neighbors, and information may then be passed along the network using a multi-hop architecture. This may be used to reduce transmit power requirements, since information is sent over shorter distances. On the other hand, receive radio power requirements may increase, since it is necessary for the receive radios to be on frequently to enable the multi-hop communication scheme.

FIG. 1A illustrates an exemplar system of wireless nodes in accordance with one embodiment. This exemplar system 100 includes wireless nodes 110-116. The nodes communicate bi-directionally with communications 120-130 (e.g., node identification information, sensor data, node status information, synchronization information, localization information, other such information for the wireless sensor network, time of flight (TOF) communications, etc.). Based on using time of flight measurements, path lengths between individual pairs of nodes can be estimated. An individual time of flight measurement between nodes 110 and 111 for example, can be achieved by sending a signal at a known time from node 110 to node 111. Node 111 receives the signal, records a time stamp of reception of the signal of the communications 120, and can then, for example, send a return signal back to A, with a time stamp of transmission of the return signal. Node 110 receives the signal and records a time stamp of reception. Based on these two transmit and receive time stamps, an average time of flight between nodes 110 and 111 can be estimated. This process can be repeated multiple times and at multiple frequencies to improve precision and to eliminate or reduce degradation due to poor channel quality at a specific frequency. A set of path lengths can be estimated by repeating this process for various node pairs. For example, in FIG. 1, the path lengths are TOF 150-160. Then, by using a geometric model, the relative position of individual nodes can be estimated based on a triangulation-like process.

This triangulation process is not feasible in a tree-like network, since only path lengths between any node and a hub can be measured. This then limits localization capability of a tree network. To preserve the energy benefits of a tree network while allowing localization, in one embodiment of this invention, a tree network for communication is combined with mesh-like network functionality for localization. Once localization is complete with mesh-like network functionality, the network switches back to tree-like communication and only time of flights between the nodes and the hub are measured periodically. Provided these time of flights are held relatively constant, the network then assumes nodes have not moved and does not waste energy is attempting to re-run mesh-based localization. On the other hand, when a change in path length in the tree network is detected, the network switches to a mesh-based system and re-triangulates to determine location of each node in the network.

In another example, a multilateration algorithm is performed to determine a location of a wireless node having an unknown location using time difference of arrival information for a plurality of nodes.

FIG. 1B shows an exemplar system of wireless nodes having multiple hubs for communicating in accordance with one embodiment. The system 700 includes a central hub 710 having a wireless control device 711, hub 720 having a wireless control device 721, hub 782 having a wireless control device 783, and additional hubs including hub n having a wireless control device n. Additional hubs which are not shown can communicate with the central hub 710, other hubs, or can be an additional central hub. Each hub communicates bi-directionally with other hubs and one or more sensor nodes. The hubs are also designed to communicate bi-directionally with other devices including device 780 (e.g., client device, mobile device, tablet device, computing device, smart appliance, smart TV, etc.).

The sensor nodes 730, 740, 750, 760, 770, 788, 792, n, and n+1 (or terminal nodes) each include a wireless device 731, 741, 751, 761, 771, 789, 793, 758, and 753, respectively. A sensor node is a terminal node if it only has upstream communications with a higher level hub or node and no downstream communications with another hub or node. Each wireless device includes RF circuitry with a transmitter and a receiver (or transceiver) to enable bi-directional communications with hubs or other sensor nodes.

In one embodiment, the central hub 710 communicates with hubs 720, 782, hub n, device 780, and nodes 760 and 770. These communications include communications 722, 724, 774, 772, 764, 762, 781, 784, 786, 714, and 712 in the wireless asymmetric network architecture. The central hub having the wireless control device 711 is configured to send communications to other hubs and to receive communications from the other hubs for controlling and monitoring the wireless asymmetric network architecture including assigning groups of nodes and a guaranteed time signal for each group.

The hub 720 communicates with central hub 710 and also sensors nodes 730, 740, and 750. The communications with these sensor nodes include communications 732, 734, 742, 744, 752, and 754. For example, from the perspective of the hub 720, the communication 732 is received by the hub and the communication 734 is transmitted to the sensor node. From the perspective of the sensor node 730, the communication 732 is transmitted to the hub 720 and the communication 734 is received from the hub.

In one embodiment, a central hub (or other hubs) assign nodes 760 and 770 to a group 716, nodes 730, 740, and 750 to a group 715, nodes 788 and 792 to a group 717, and nodes n and n+1 to a group n. In another example, groups 716 and 715 are combined into a single group.

By using the architecture illustrated in FIG. 1, nodes requiring long battery life minimize the energy expended on communication and higher level nodes in the tree hierarchy are implemented using available energy sources or may alternatively use batteries offering higher capacities or delivering shorter battery life. To facilitate achievement of long battery life on the battery-operated terminal nodes, communication between those nodes and their upper level counterparts (hereafter referred to as lowest-level hubs) may be established such that minimal transmit and receive traffic occurs between the lowest-level hubs and the terminal nodes.

In one embodiment, the nodes spend most of their time (e.g., more than 90% of their time, more than 95% of their time, approximately 98% or more than 99% of their time) in a low-energy non-communicative state. When the node wakes up and enters a communicative state, the nodes are operable to transmit data to the lowest-level hubs. This data may include node identification information, sensor data, node status information, synchronization information, localization information and other such information for the wireless sensor network.

To determine the distance between two objects based on RF, ranging measurements are performed (i.e., RF communication is used to estimate the distance between the pair of objects). To achieve this, an RF signal is sent from one device to another. FIGS. 3-8C of U.S. patent application Ser. No. 15/173,531 illustrate embodiments of time of flight measurement systems.

Time of flight measurements are inherently sensitive to the timing of operations within the network, and therefore, the clocking of the devices performing the measurements is important. In one embodiment, a node at an unknown location can be located via TDoA without a shared clock. The receive nodes are synchronized using an additional transaction between the known nodes. Note that the locations of the known nodes can be determined using localization as described in the U.S. patent application Ser. No. 15/173,531.

FIG. 2A illustrates a system for localization of nodes utilizing time difference of arrival in accordance with one embodiment. The system 200 is configured to have one master node 210 (M210), one node 240 at unknown location (N240), and sniff nodes (e.g., S220, 230, etc.). The master node 210 first performs two way time of flight with RTT and fractional distance (as described in the U.S. patent application Ser. No. 15/173,531) to each of the sniff nodes For example, FIG. 2B illustrates an asynchronous system that is used for time of flight estimation in accordance with one embodiment. A device 810 first sends a RF signal 812 having a packet to device 820 at time T1. The packet arrives at the device 820 at time T2, triggering the packet detection algorithm in device 820 to register this time. Device 820 then sends back a signal 822 having a packet at time T3, which arrives at device 810 at time T4 and triggers the device 810 to register the time and process the waveform. Notice that unlike the case of fully synchronous system, T1 and T4 are times recorded on device 810 and therefore is referenced to its reference clock. T2 and T3 are recorded based on the time reference of device 820. The coarse time estimation is done as 2×ToF=(T4−T1)−(T3−T2)

Because T4 and T1 are sampled at the same clock, there is no arbitrary phase between T4 and T1. Therefore, T4−T1 is accurate in time; the same principle applies to T3−T2. Therefore, this measurement is immune to any phase-walking between the two devices resulting from the asynchronous nature of this system. Similar to the previous embodiment, this measurement is limited by the resolution of the sampling clock period of T1/T2/T3/T4. In order to improve this accuracy, a frequency response measurement can be performed on both devices. Device 820 measures the channel response using the packet from device 810 and device 810 measures the channel response using the packet from device 820. Because the two devices are not synchronous, there is an uncertainty in the phase between the two clocks, annotated as T_(offset) here. This phase offset of the clock manifests itself as an extra phase of the channel response measurement on each side, but it can be eliminated by multiplying the channel responses from the two sides. Assuming the channel response is the same as before, then the measurement from device 820 will be H ₈₂₀(f)=H(f)^(e−j2πfToffset)

The measurement from the device 810 will be H ₈₁₀(f)=H(f)^(e+j2πfToffset)

The combined channel response is therefore H ₈₁₀(f)H ₈₂₀(f)=H(f)²=(ΣA _(k) e ^(−j2πΔTk))²

which cancels out the phase difference between the two clocks. Similar to the previous embodiment, algorithms such as matrix pencil, MUSIC, etc. can be used to estimate the delay from H₈₁₀(f)H₈₂₀(f), which produces the 2 min{ΔT_(k)}, and the distance measurement is given by Distance=[(T4−T1)/2−(T3−T2)/2−S{H ₈₁₀(f)H ₈₂₀(f)}/2]×C

Alternatively T_(offset) can be estimated from H ₈₁₀(f)H ₈₂₀(f)=e ^(+2j2πfToffset)

The T_(offset) is half the phase slope of the divided channel responses. The channel response in either direction can be corrected by the calculated offset. The distance estimation can then be calculated as Distance=[(T4−T1)/2−(T3−T2)/2−S{H ₈₁₀(f)}−T _(offset)]×C Or Distance=[(T4−T1)/2−(T3−T2)/2−S{H ₈₂₀(f)}−T _(offset)]×C

This method has advantages over the multiplication method. The H(f)² channel response includes terms at double the amplitude and distance of each path as well as cross terms for every 2 path permutation. That is for a 2 path case, A₈₁₀ ²e^(j2πf2ΔT1), A₈₂₀ ²e^(j2πf2ΔT2), and A₈₁₀A₈₂₀e^(j2πf(ΔT1+ΔT2)). The fine estimation methods are more effective and more robust to noise when applied to the unidirectional channel response H(f) as there are less paths to distinguish and lower dynamic range.

The aforementioned short path elimination algorithm can also be used in asynchronous systems such as those disclosed above

As shown above, in an asynchronous system, the information from the two devices needs to be combined for calculation. In order to do that, in one embodiment, one of the devices can send the information to the other device, either using the same RF signals (e.g., 812, 822, 1022, 1023) mentioned before, or using an independent RF signal path 1024, as shown in FIG. 2C in one embodiment of a 2-way ToF measurement system 1000.

FIG. 3 illustrates a timing diagram for communications of the system 200 in accordance with one embodiment. N240 is configured to send a communication (e.g., transmitted packet) that is received as packets 241-243 (e.g., acknowledgement packet) in response to the communication 212 (e.g., unicast packets) from the master node 210. This system is set up utilizing the master node as an access point (AP) and having the unknown node (e.g., sensor node, mobile device, smart device, smart watch, etc.) associated with it or by other means. The sniff nodes 220 and 230 are configured to receive any packets sent by the master node or N240. The master node sends a communication 212 (e.g., forward packet) to N240 at time T₁. N240 receives this communication 212 at time T₂. Each of the sniff nodes records a detection timestamp and channel sense information (CSI) of a received communication (e.g., node 220 receives forward packet 202 at time T₃, node 230 receives forward packet 204 at time T₄). The packets 202, 204, and 212 originate from the same communication from M210. The unknown node N240 transmits a communication that is received as packets 241-243 (e.g., acknowledgement packets at time T₅) in response to receiving the communication 212. The sniff nodes and the master node all record a timestamp and CSI of the received communications 241-243 (e.g., acknowledgement packets received at time T₆, T₇, T₈).

The master to sniff ToF and the timestamp and CSI information at the master and sniff nodes can then be combined to determine the location of node 240. The T_(DOA) between the master and each sniff node is calculated in accordance with equation 1 below. Then these TDoA values can be used in a standard TDoA multilateration algorithm to determine the location of N240.

The TDoA between each sniff node and the master node is determined as follows. In an ideal case, the TDoA is simply a delta between a first time T₆ when the master node receives the acknowledge packets from node 240 and a second time T₇ when the sniff nodes receive the acknowledgement packets from the node 240.

However, the master and sniff nodes have independent clocks references with counter offsets as well as phase and frequency offsets from each other. To resolve this, in one example, a packet transmission time of the communication 212 (e.g., forward packets 212 at time T₁) at the master node is used as the time reference for both the master node and sniff nodes.

$\begin{matrix} \begin{matrix} {T_{{DoA}\mspace{14mu} M\; 210\text{-}S\; 220} =} & {T_{6} - T_{7}} \\ {=} & {\left( {T_{6} - T_{1}} \right) - \left( {T_{7} - T_{1}} \right)} \\ {=} & {\left( {T_{6} - T_{1}} \right) - \left( {T_{7} - \left( {T_{3} - T_{{oF}\mspace{14mu} M\; 210\text{-}S\; 220}} \right)} \right.} \\ {=} & {\left( {{RTT}_{M\; 210} -_{N\; 240\mspace{14mu}{sampling}} +} \right.} \\  & {\left. T_{{frac}\mspace{14mu} M\; 210\text{-}N\; 240} \right) -} \\  & {\left( {T_{S\; 220\mspace{14mu}{Ack}\mspace{14mu}{Rx}\mspace{14mu}{sampling}} +} \right.} \\  & {T_{S\; 220\mspace{14mu}{Ack}\mspace{14mu}{Rx}\mspace{14mu}{frac}} -} \\  & {\left( {T_{S\; 220\mspace{14mu}{forw}\mspace{14mu}{Rx}\mspace{14mu}{sampling}} +} \right.} \\  & {T_{S\; 220\mspace{14mu}{forw}\mspace{14mu}{Rx}\mspace{14mu}{frac}} -} \\  & \left. \left. T_{{oF}\mspace{14mu} M\; 210\text{-}S\; 220} \right) \right) \end{matrix} & {{Equation}\mspace{14mu} 1} \end{matrix}$

The time of the sniff nodes receiving communications 242 and 243 (e.g., sniff acknowledgement reception) can be aligned to the master forward packet transmissions by subtracting a timestamp of the acknowledgement forward reception for receiving communications 242 and 243 and the previously measured ToF calculated between the master and sniff node.

The time resolution of the TDoA can be finer than the rate of the sampling clock by using the channel sense information (CSI) for a fractional sample estimate of each packet reception. The CSI can be used to calculate the fractional sample estimate by using the slope of the phase (in a single line of sight path) or using techniques such as matrix pencil, MUSIC, or IFFT. FIGS. 2 and 3 and equation 1 show an example of the system and how the TDoA is calculated. Equation 2 shows how the delays introduced from differences in the reference clocks are cancelled.

$\begin{matrix} {{T_{6}^{\prime} = {{T\; 6} + t_{{dM}\; 210\text{-}N\; 240} + t_{{dN}\; 240\text{-}M\; 210}}}{T_{7}^{\prime} = {T_{7} + t_{{dS}\; 220\text{-}N\; 240} + t_{{dN}\; 240\text{-}M\; 210}}}{T_{3}^{\prime} = {T_{3} + t_{{dS}\; 220\text{-}M\; 210}}}\begin{matrix} {T_{DoA}^{\prime} =} & {T_{6}^{\prime} - T_{7}^{\prime}} \\ {=} & {T_{DoA} + t_{{dM}\; 210\text{-}N\; 240} + t_{{dN}\; 240\text{-}M\; 210} -} \\  & {t_{{dS}\; 220\text{-}N\; 240} - t_{{dN}\; 240\text{-}M\; 210} + t_{{dS}\; 220\text{-}M\; 210}} \end{matrix}{{Note}\text{:}\mspace{14mu}\begin{matrix} {t_{{dS}\; 220\text{-}M\; 210} = {t_{{dS}\; 220\text{-}N\; 240} + t_{{dN}\; 240\text{-}M\; 210}}} \\ {= {t_{{dS}\; 220\text{-}N\; 240} - t_{{dM}\; 210\text{-}N\; 240}}} \end{matrix}}{{t_{{dS}\; 220\text{-}M\; 210} - t_{{dS}\; 220\text{-}N\; 240} + t_{{dM}\; 210\text{-}N\; 240}} = 0}{T_{DoA}^{\prime} = T_{DoA}}} & {{Equation}\mspace{14mu} 2} \end{matrix}$

To improve signal to noise ratio (SNR), the process can be repeated with multiple packets. The TDoA can be calculated per packet and then averaged. Alternatively, the timestamps and CSIs can be averaged before combining. To average CSIs, the magnitudes and phases must be averaged independently and then combined. By configuring the system again with a different unknown node, the locations of multiple nodes can be found.

FIG. 4 illustrates a system for localization of nodes utilizing time difference of arrival in accordance with an alternative embodiment. The system 400 is configured to have one master node 410 (M410), one node 440 at unknown location (N440), and sniff nodes (e.g., S420, S430, etc.). FIG. 5 illustrates a timing diagram for communications of the system 400 in accordance with one embodiment. The unknown node N440 can initiate the packet transaction. N440 sends a communication 441 (e.g., forward packet 441) to the master (M) node 410 at time T₁. The master node 410 receives the communication 441 at time T₂. The master node 410 responds with a communication 412 (e.g., an acknowledgement packet 412) at time T₅. The sniff nodes 420 and 430 listen to the communications 442-443 at times T₄ and T₃ (e.g., forward packets 442-443) from N440 and the communications 402 and 404 (e.g., acknowledgement packet 402 and 404) from the master node 410. The sniff node 420 receives the communication 443 at time T₃ and receives the communication 402 at time T₆. The sniff node 430 receives the communication 442 at time T₄ and receives the communication 404 at time T₇. The received packets 441-443 originate from the same communication from N440.

The TDoA is now calculated based on the arrival of the forward packets at the master and sniff nodes from N440. The packet transmission time of the acknowledgement packets from the master node is now used to align the timing between the nodes in accordance with Equation 3 with delta offset equaling T₆−T₅−T_(oFM410-S420):

$\begin{matrix} {T_{{DoA}\mspace{14mu} M\; 410\text{-}S\; 420} =} & {T_{2} - T_{3}^{M\; 410}} \\ {=} & {T_{2} - T_{3} - {{delta}\mspace{14mu}{offset}\mspace{14mu}{between}}} \\  & {{clocks}\mspace{14mu}{of}\mspace{14mu} M\; 410\mspace{14mu}{and}\mspace{14mu} S\; 420} \\ {=} & {\left( {T_{2} - T_{3}} \right) + T_{6} - T_{5} - T_{{oF}\mspace{14mu} M\; 410\text{-}S\; 420}} \\ {=} & {\left( {T_{2\mspace{14mu}{sampling}} +_{T\; 2{frac}}{- T_{3\;{sampling}}} -} \right.} \\  & {\left. T_{3\mspace{14mu}{frac}} \right) + T_{6\mspace{14mu}{sampling}} + T_{6\mspace{14mu}{frac}} -} \\  & {T_{5\mspace{14mu}{sampling}} - T_{5\mspace{14mu}{frac}} - T_{{oF}\mspace{14mu} M\; 410\text{-}S\; 420}} \end{matrix}$

FIG. 6 illustrates a method for determining location estimation of nodes using time difference of arrival techniques in accordance with one embodiment. The operations of method 600 may be executed by a wireless device, a wireless control device of a hub (e.g., an apparatus), or system, which includes processing circuitry or processing logic. The processing logic may include hardware (circuitry, dedicated logic, etc.), software (such as is run on a general purpose computer system or a dedicated machine or a device), or a combination of both. In one embodiment, a hub performs the operations of method 600.

Upon initialization of a wireless network architecture, at operation 601, the processing logic of a system is configured to have a first node (e.g., master node), second and third wireless nodes (e.g., sniff nodes), and a fourth node (e.g., sensor node, mobile device, smart device, smart watch, etc.) at an unknown location. The first node (e.g., master node) performs two way time of flight with RTT and fractional distance (as described in the U.S. patent application Ser. No. 15/173,531) with of the second and third nodes (e.g., sniff nodes) the sniff nodes at operation 602.

At operation 604, the first node transmits a communication with a forward packet to the second, third, and fourth nodes at a first time. At operation 606, the fourth node receives this communication at a second time. At operation 608, the second and third nodes receive these communications at a third time and a fourth time, respectively. At operation 610, the fourth node is configured to send a communication with an acknowledgement packet to the first, second, and third nodes at a fifth time in response to the communication (e.g., forward packet) from the first node. In one example, this system is set up utilizing the master node as an access point (AP) and having the unknown fourth node associated with it or by other means. The sniff nodes are configured to receive any packets sent by the master node or unknown fourth node. Each of the sniff nodes records a detection timestamp and channel sense information (CSI) of a received communication. The sniff nodes and the master node all record a timestamp and CSI of the received communications (e.g., acknowledgement packets received at sixth, seventh, eighth times) at operation 612.

The master to sniff ToF and the timestamp and CSI information at the master and sniff nodes can then be combined to determine the location of the unknown fourth node at operation 614. The T_(DoA) between the master and each sniff node is calculated in accordance with equation 1. Then these TDoA values can be used in a standard TDoA multilateration algorithm to determine the location of N240.

In one example, the TDoA algorithms discussed herein are used to locate a fourth node (e.g., sensor node, mobile device, smart device, smart watch, robot, etc.) at an unknown location. Thus, a user of the fourth node can locate this node without having to search for the node.

The communication between hubs and nodes as discussed herein may be achieved using a variety of means, including but not limited to direct wireless communication using radio frequencies, Powerline communication achieved by modulating signals onto the electrical wiring within the house, apartment, commercial building, etc., WiFi communication using such standard WiFi communication protocols as 802.11a, 802.11b, 802.11n, 802.11ac, and other such Wifi Communication protocols as would be apparent to one of ordinary skill in the art, cellular communication such as GPRS, EDGE, 3G, HSPDA, LTE, and other cellular communication protocols as would be apparent to one of ordinary skill in the art, Bluetooth communication, communication using well-known wireless sensor network protocols such as Zigbee, and other wire-based or wireless communication schemes as would be apparent to one of ordinary skill in the art.

The implementation of the radio-frequency communication between the terminal nodes and the hubs may be implemented in a variety of ways including narrow-band, channel overlapping, channel stepping, multi-channel wide band, and ultra-wide band communications.

The hubs may be physically implemented in numerous ways in accordance with embodiments of the invention. FIG. 7A shows an exemplary embodiment of a hub implemented as an overlay 1500 for an electrical power outlet in accordance with one embodiment. The overlay 1500 (e.g., faceplate) includes a hub 1510 and a connection 1512 (e.g., communication link, signal line, electrical connection, etc.) that couples the hub to the electrical outlet 1502. Alternatively (or additionally), the hub is coupled to outlet 1504. The overlay 1500 covers or encloses the electrical outlets 1502 and 1504 for safety and aesthetic purposes.

FIG. 7B shows an exemplary embodiment of an exploded view of a block diagram of a hub 1520 implemented as an overlay for an electrical power outlet in accordance with one embodiment. The hub 1520 includes a power supply rectifier 1530 that converts alternating current (AC), which periodically reverses direction, to direct current (DC) which flows in only one direction. The power supply rectifier 1530 receives AC from the outlet 1502 via connection 1512 (e.g., communication link, signal line, electrical connection, etc.) and converts the AC into DC for supplying power to a controller circuit 1540 via a connection 1532 (e.g., communication link, signal line, electrical connection, etc.) and for supplying power to RF circuitry 1550 via a connection 1534 (e.g., communication link, signal line, electrical connection, etc.). The controller circuit 1540 includes memory 1542 or is coupled to memory that stores instructions which are executed by processing logic 1544 (e.g., one or more processing units) of the controller circuit 1540 for controlling operations of the hub for forming, monitoring, and performing localization of the wireless asymmetrical network as discussed herein. The RF circuitry 1550 may include a transceiver or separate transmitter 1554 and receiver 1556 functionality for sending and receiving bi-directional communications via antenna(s) 1552 with the wireless sensor nodes. The RF circuitry 1550 communicates bi-directionally with the controller circuit 1540 via a connection 1534 (e.g., communication link, signal line, electrical connection, etc.). The hub 1520 can be a wireless control device 1520 or the controller circuit 1540, RF circuitry 1550, and antenna(s) 1552 in combination may form the wireless control device as discussed herein.

FIG. 8A shows an exemplary embodiment of a hub implemented as a card for deployment in a computer system, appliance, or communication hub in accordance with one embodiment. The card 1662 can be inserted into the system 1660 (e.g., computer system, appliance, or communication hub) as indicated by arrow 1663.

FIG. 8B shows an exemplary embodiment of a block diagram of a hub 1664 implemented as a card for deployment in a computer system, appliance, or communication hub in accordance with one embodiment. The hub 1664 includes a power supply 1666 that provides power (e.g., DC power supply) to a controller circuit 1668 via a connection 1674 (e.g., communication link, signal line, electrical connection, etc.) and provides power to RF circuitry 1670 via a connection 1676 (e.g., communication link, signal line, electrical connection, etc.). The controller circuit 1668 includes memory 1661 or is coupled to memory that stores instructions which are executed by processing logic 1663 (e.g., one or more processing units) of the controller circuit 1668 for controlling operations of the hub for forming, monitoring, and performing localization of the wireless asymmetrical network as discussed herein. The RF circuitry 1670 may include a transceiver or separate transmitter 1675 and receiver 1677 functionality for sending and receiving bi-directional communications via antenna(s) 1678 with the wireless sensor nodes. The RF circuitry 1670 communicates bi-directionally with the controller circuit 1668 via a connection 1672 (e.g., communication link, signal line, electrical connection, etc.). The hub 1664 can be a wireless control device 1664 or the controller circuit 1668, RF circuitry 1670, and antenna(s) 1678 in combination may form the wireless control device as discussed herein.

FIG. 8C shows an exemplary embodiment of a hub implemented within an appliance (e.g., smart washing machine, smart refrigerator, smart thermostat, other smart appliances, etc.) in accordance with one embodiment. The appliance 1680 (e.g., smart washing machine) includes a hub 1682.

FIG. 8D shows an exemplary embodiment of an exploded view of a block diagram of a hub 1684 implemented within an appliance (e.g., smart washing machine, smart refrigerator, smart thermostat, other smart appliances, etc.) in accordance with one embodiment. The hub includes a power supply 1686 that provides power (e.g., DC power supply) to a controller circuit 1690 via a connection 1696 (e.g., communication link, signal line, electrical connection, etc.) and provides power to RF circuitry 1692 via a connection 1698 (e.g., communication link, signal line, electrical connection, etc.). The controller circuit 1690 includes memory 1691 or is coupled to memory that stores instructions which are executed by processing logic 1688 (e.g., one or more processing units) of the controller circuit 1690 for controlling operations of the hub for forming, monitoring, and performing localization of the wireless asymmetrical network as discussed herein. The RF circuitry 1692 may include a transceiver or separate transmitter 1694 and receiver 1695 functionality for sending and receiving bi-directional communications via antenna(s) 1699 with the wireless sensor nodes. The RF circuitry 1692 communicates bi-directionally with the controller circuit 1690 via a connection 1689 (e.g., communication link, signal line, electrical connection, etc.). The hub 1684 can be a wireless control device 1684 or the controller circuit 1690, RF circuitry 1692, and antenna(s) 1699 in combination may form the wireless control device as discussed herein.

In one embodiment, an apparatus (e.g., hub) for providing a wireless asymmetric network architecture includes a memory for storing instructions, processing logic (e.g., one or more processing units, processing logic 1544, processing logic 1663, processing logic 1688, processing logic 1763, processing logic 1888) of the hub to execute instructions to establish and control communications in a wireless asymmetric network architecture, and radio frequency (RF) circuitry (e.g., RF circuitry 1550, RF circuitry 1670, RF circuitry 1692, RF circuitry 1890) including multiple antennas (e.g., antenna(s) 1552, antenna(s) 1678, antenna(s) 1699, antennas 1311, 1312, and 1313, etc.) to transmit and receive communications in the wireless asymmetric network architecture. The RF circuitry and multiple antennas to transmit communications to a plurality of sensor nodes (e.g., node 1, node 2) each having a wireless device with a transmitter and a receiver (or transmitter and receiver functionality of a transceiver) to enable bi-directional communications with the RF circuitry of the apparatus in the wireless asymmetric network architecture.

In one example, a memory for storing instructions includes one or more processing units to execute instructions for controlling a plurality of sensor nodes in a wireless network architecture and determining locations of the plurality of sensor nodes and radio frequency (RF) circuitry to transmit communications to and receive communications from the plurality of sensor nodes each having a wireless device with a transmitter and a receiver to enable bi-directional communications with the RF circuitry of the apparatus in the wireless network architecture. The one or more processing units of the apparatus are configured to execute instructions to transmit a communication to first, second, and third wireless nodes, to receive a communication with an acknowledgement packet from the third node that has an unknown location, and to determine time difference of arrival information between the apparatus and the first wireless node and between the apparatus and the second wireless node.

In one example, the apparatus is powered by a mains electrical source and the plurality of sensor nodes are each powered by a battery source to form the wireless network architecture.

Various batteries could be used in the wireless sensor nodes, including lithium-based chemistries such as Lithium Ion, Lithium Polymer, Lithium Phosphate, and other such chemistries as would be apparent to one of ordinary skill in the art. Additional chemistries that could be used include Nickel metal hydride, standard alkaline battery chemistries, Silver Zinc and Zinc Air battery chemistries, standard Carbon Zinc battery chemistries, lead Acid battery chemistries, or any other chemistry as would be obvious to one of ordinary skill in the art.

The present invention also relates to an apparatus for performing the operations described herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions.

The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the required method operations.

FIG. 15 illustrates a block diagram of a sensor node in accordance with one embodiment. The sensor node 1700 includes a power source 1710 (e.g., energy source, battery source, primary cell, rechargeable cell, etc.) that provides power (e.g., DC power supply) to a controller circuit 1720 via a connection 1774 (e.g., communication link, signal line, electrical connection, etc.), provides power to RF circuitry 1770 via a connection 1776 (e.g., communication link, signal line, electrical connection, etc.), and provides power to sensing circuitry 1740 via a connection 1746 (e.g., communication link, signal line, electrical connection, etc.). The controller circuit 1720 includes memory 1761 or is coupled to memory that stores instructions which are executed by processing logic 1763 (e.g., one or more processing units) of the controller circuit 1720 for controlling operations of the sensor node for forming and monitoring the wireless asymmetrical network as discussed herein. The RF circuitry 1770 (e.g., communication circuitry) may include a transceiver or separate transmitter 1775 and receiver 1777 functionality for sending and receiving bi-directional communications via antenna(s) 1778 with the hub(s) and optional wireless sensor nodes. The RF circuitry 1770 communicates bi-directionally with the controller circuit 1720 via a connection 1772 (e.g., electrical connection). The sensing circuitry 1740 includes various types of sensing circuitry and sensor(s) including image sensor(s) and circuitry 1742, moisture sensor(s) and circuitry 1743, temperature sensor(s) and circuitry, humidity sensor(s) and circuitry, air quality sensor(s) and circuitry, light sensor(s) and circuitry, motion sensor(s) and circuitry 1744, audio sensor(s) and circuitry 1745, magnetic sensor(s) and circuitry 1746, and sensor(s) and circuitry n, etc.

The wireless localization techniques disclosed herein may be combined with other sensed information to improve localization accuracy of the overall network. For example, in wireless sensors in which one or more of the nodes contain cameras, captured images can be used with image processing and machine learning techniques to determine whether the sensor nodes that are being monitored are looking at the same scene and are therefore likely in the same room. Similar benefits can be achieved by using periodic illumination and photodetectors. By strobing the illumination and detecting using the photodetectors, the presence of an optical path can be detected, likely indicating the absence of opaque walls between the strobe and the detector. In other embodiments, magnetic sensors can be integrated into the sensor nodes and used as a compass to detect the orientation of the sensor node that is being monitored. This information can then be used along with localization information to determine whether the sensor is on the wall, floor, ceiling, or other location.

In one example, each sensor node may include an image sensor and each perimeter wall of a house includes one or more sensor nodes. A hub analyzes sensor data including image data and optionally orientation data along with localization information to determine absolute locations for each sensor node. The hub can then build a three dimensional image of each room of a building for a user. A floor plan can be generated with locations for walls, windows, doors, etc. Image sensors may capture images indicating a change in reflections that can indicate home integrity issues (e.g., water, leaking roof, etc.).

FIG. 10 illustrates a block diagram of a system 1800 having a hub in accordance with one embodiment. The system 1800 includes or is integrated with a hub 1882 or central hub of a wireless asymmetric network architecture. The system 1800 (e.g., computing device, smart TV, smart appliance, communication system, etc.) may communicate with any type of wireless device (e.g., cellular phone, wireless phone, tablet, computing device, smart TV, smart appliance, etc.) for sending and receiving wireless communications. The system 1800 includes a processing system 1810 that includes a controller 1820 and processing units 1814. The processing system 1810 communicates with the hub 1882, an Input/Output (I/O) unit 1830, radio frequency (RF) circuitry 1870, audio circuitry 1860, an optics device 1880 for capturing one or more images or video, an optional motion unit 1844 (e.g., an accelerometer, gyroscope, etc.) for determining motion data (e.g., in three dimensions) for the system 1800, a power management system 1840, and machine-accessible non-transitory medium 1850 via one or more bi-directional communication links or signal lines 1898, 1818, 1815, 1816, 1817, 1813, 1819, 1811, respectively.

The hub 1882 includes a power supply 1891 that provides power (e.g., DC power supply) to a controller circuit 1884 via a connection 1885 (e.g., communication link, signal line, electrical connection, etc.) and provides power to RF circuitry 1890 via a connection 1887 (e.g., communication link, signal line, electrical connection, etc.). The controller circuit 1884 includes memory 1886 or is coupled to memory that stores instructions which are executed by processing logic 1888 (e.g., one or more processing units) of the controller circuit 1884 for controlling operations of the hub for forming and monitoring the wireless asymmetrical network as discussed herein. The RF circuitry 1890 may include a transceiver or separate transmitter (TX) 1892 and receiver (RX) 1894 functionality for sending and receiving bi-directional communications via antenna(s) 1896 with the wireless sensor nodes or other hubs. The RF circuitry 1890 communicates bi-directionally with the controller circuit 1884 via a connection 1889 (e.g., communication link, signal line, electrical connection, etc.). The hub 1882 can be a wireless control device 1884 or the controller circuit 1884, RF circuitry 1890, and antenna(s) 1896 in combination may form the wireless control device as discussed herein.

RF circuitry 1870 and antenna(s) 1871 of the system or RF circuitry 1890 and antenna(s) 1896 of the hub 1882 are used to send and receive information over a wireless link or network to one or more other wireless devices of the hubs or sensors nodes discussed herein. Audio circuitry 1860 is coupled to audio speaker 1862 and microphone 1064 and includes known circuitry for processing voice signals. One or more processing units 1814 communicate with one or more machine-accessible non-transitory mediums 1850 (e.g., computer-readable medium) via controller 1820. Medium 1850 can be any device or medium (e.g., storage device, storage medium) that can store code and/or data for use by one or more processing units 1814. Medium 1850 can include a memory hierarchy, including but not limited to cache, main memory and secondary memory.

The medium 1850 or memory 1886 stores one or more sets of instructions (or software) embodying any one or more of the methodologies or functions described herein. The software may include an operating system 1852, network services software 1856 for establishing, monitoring, and controlling wireless asymmetric network architectures, communications module 1854, and applications 1858 (e.g., home or building security applications, home or building integrity applications, developer applications, etc.). The software may also reside, completely or at least partially, within the medium 1850, memory 1886, processing logic 1888, or within the processing units 1814 during execution thereof by the device 1800. The components shown in FIG. 18 may be implemented in hardware, software, firmware or any combination thereof, including one or more signal processing and/or application specific integrated circuits.

Communication module 1854 enables communication with other devices. The I/O unit 1830 communicates with different types of input/output (I/O) devices 1834 (e.g., a display, a liquid crystal display (LCD), a plasma display, a cathode ray tube (CRT), touch display device, or touch screen for receiving user input and displaying output, an optional alphanumeric input device).

Any of the following examples can be combined into a single embodiment or these examples can be separate embodiments. In one example, an asynchronous system for localization of nodes in a wireless network architecture comprises first and second wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture; and a wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first and second, wireless nodes in the wireless network architecture. The one or more processing units of the first wireless node are configured to execute instructions to transmit a communication to the second wireless node and the wireless node with the unknown location, to receive a communication with an acknowledgement packet from the wireless node, and to determine time difference of arrival information between the first and second wireless nodes.

In another example, the system includes a third wireless node having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture. The one or more processing units of the first wireless node are configured to execute instructions for a multilateration algorithm to determine a location of the wireless node with the unknown location using the time difference of arrival information between the first and second wireless nodes and also between the first and third wireless nodes.

In another example, the first wireless node has a first reference clock signal and the second wireless node has a second reference clock signal.

In another example, one or more processing units of the wireless node having an unknown location are configured to execute instructions to transmit communications including acknowledgement packets to the first, second, and third wireless nodes in response to receiving a communication with a forward packet from the first node.

In another example, one or more processing units of the second and third wireless nodes are configured to execute instructions to receive communications including forward packets from the first wireless node and acknowledgement packets from the fourth wireless node, to record a timestamp and channel sense information for each of the received forward and acknowledgement packets.

In another example, a transmission time of a forward packet from the first wireless node is used as a time reference for the first, second, and third wireless nodes.

In another example, the time difference of arrival information between the first and second wireless nodes is determined based on a first time when the first wireless node receives the acknowledgement packet from the fourth wireless node, a second time when the second wireless node receives the acknowledgement packet from the fourth wireless node, and the time reference.

In another example, the one or more processing units of the first wireless node are configured to execute instructions to determine a difference between the first time and the time reference and also determine a difference between the second time and the time reference.

In another example, the one or more processing units of the first wireless node are configured to execute instructions to determine the time difference of arrival information based on determining time of flight estimates for localization that is based on time estimates of round trip time of communications between the first and second wireless nodes and communications between the first and third wireless nodes.

In one example, an apparatus comprises a memory for storing instructions, one or more processing units to execute instructions for controlling a plurality of sensor nodes in a wireless network architecture and determining locations of the plurality of sensor nodes and radio frequency (RF) circuitry to transmit communications to and receive communications from the plurality of sensor nodes each having a wireless device with a transmitter and a receiver to enable bi-directional communications with the RF circuitry of the apparatus in the wireless network architecture. The one or more processing units of the apparatus are configured to execute instructions to transmit a communication to first, second, and third wireless nodes, to receive a communication with an acknowledgement packet from the third node that has an unknown location, and to determine time difference of arrival information between the apparatus and the first wireless node and between the apparatus and the second wireless node.

In another example, the one or more processing units of the apparatus are configured to execute instructions for a multilateration algorithm to determine a location of the third wireless node using the time difference of arrival information.

In another example, the apparatus has a first reference clock signal and the first wireless node has a second reference clock signal.

In another example, the transmitted communication includes a transmission time of a forward packet that is transmitted to the first, second, and third wireless nodes with the transmission time being used as a time reference for the apparatus, the first wireless node, and the second wireless node.

In another example, the time difference of arrival information between the apparatus and the first wireless node is determined based on a first time when the apparatus receives an acknowledgement packet from the third wireless node, a second time when the first wireless node receives an acknowledgement packet from the third wireless node, and the time reference.

In another example, the one or more processing units of the apparatus are configured to execute instructions to determine a difference between the first time and the time reference and also determine a difference between the second time and the time reference.

In one example, a system for localization of nodes in a wireless network architecture includes first, second, and third wireless nodes each having a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture and a fourth wireless node having an unknown location and a wireless device with a transmitter and a receiver to enable communications with the first, second, and third wireless nodes in the wireless network architecture. The one or more processing units of the first wireless node are configured to execute instructions to receive a communication with a forward packet from the fourth node, to transmit a communication to the second, third, and fourth wireless nodes in response to the forward packet, and to determine time difference of arrival information between the first and second wireless nodes and between the first and third wireless nodes.

In another example, the one or more processing units of the first wireless node are configured to execute instructions for a multilateration algorithm to determine a location of the fourth wireless node using the time difference of arrival information.

In another example, the first wireless node has a first reference clock signal and the second wireless node has a second reference clock signal.

In another example, one or more processing units of the fourth wireless node are configured to execute instructions to transmit a communication including a forward packet to the first, second, and third wireless nodes.

In another example, one or more processing units of the second and third wireless nodes are configured to execute instructions to receive communications including forward packets from the fourth wireless node and acknowledgement packets from the first wireless node and to record a timestamp and channel sense information for each of the received forward and acknowledgement packets.

In another example, the time difference of arrival information between the first and second wireless nodes is determined based on a first time when the first wireless node receives a forward packet from the fourth wireless node, a second time when the second wireless node receives a forward packet from the fourth wireless node, and a time offset between the first and second reference clock signals.

In another example, the one or more processing units of the first wireless node are configured to execute instructions to determine the time offset between the first and second reference clock signals based on a third time when the second wireless node receives an acknowledgement packet from the first wireless node, a fourth time when the first wireless node transmits an acknowledgement packet to the second wireless node, and time of flight estimates for communications between the first and second wireless nodes.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 

What is claimed is:
 1. An asynchronous system for localization of nodes in a wireless network architecture, comprising: first and second wireless nodes each having known locations and including a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture; and a wireless sensor node having an unknown location and including a wireless device with RF circuitry to enable communications with the first and the second wireless nodes in the wireless network architecture, wherein the one or more processing units of the first wireless node are configured to execute instructions to transmit a first communication to the second wireless node and the wireless sensor node, to receive a second communication with an acknowledgement packet from the wireless sensor node, and to determine time difference of arrival information of the reception of the second communication between each of the first and the second wireless nodes, wherein a transmission time of the first communication being transmitted from the first wireless node to the wireless sensor node is used as a time reference for each of the first and the second wireless nodes.
 2. The asynchronous system of claim 1, further comprising: a third wireless node including a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture wherein the one or more processing units of the first wireless node are configured to execute instructions for a multilateration algorithm to determine a location of the wireless sensor node using the time difference of arrival information between the first and the second wireless nodes and also between the first and the third wireless nodes.
 3. The asynchronous system of claim 1, wherein the first wireless node has a first reference clock signal and the second wireless node has a second reference clock signal.
 4. The asynchronous system of claim 2, wherein one or more processing units of the wireless sensor node are configured to execute instructions to transmit the second communication including the acknowledgement packet to the first, the second, and the third wireless nodes in response to receiving the first communication with a forward packet from the first node.
 5. The asynchronous system of claim 4, wherein one or more processing units of the second and the third wireless nodes are configured to execute instructions to receive communications including forward packets from the first wireless node and acknowledgement packets from the wireless sensor node, to record a timestamp and channel sense information for each of the received forward and acknowledgement packets.
 6. The asynchronous system of claim 5, wherein a transmission time of the forward packet from the first wireless node is used as a time reference for the first, the second, and the third wireless nodes.
 7. The asynchronous system of claim 6, wherein the time difference of arrival information between the first and the second wireless nodes is determined based on a first time when the first wireless node receives the acknowledgement packet from the wireless sensor node, a second time when the second wireless node receives the acknowledgement packet from the wireless sensor node, and the time reference.
 8. The asynchronous system of claim 7, wherein the one or more processing units of the first wireless node are configured to execute instructions to determine a difference between the first time and the time reference and also determine a difference between the second time and the time reference.
 9. The asynchronous system of claim 7, wherein the one or more processing units of the first wireless node are configured to execute instructions to determine the time difference of arrival information based on determining time of flight estimates for localization that are based on time estimates of round trip time of communications between the first and the second wireless nodes and communications between the first and the third wireless nodes.
 10. An apparatus, comprising: a memory for storing instructions; one or more processing units to execute instructions for controlling a plurality of wireless sensor nodes in a wireless network architecture and asynchronously determining locations of the plurality of wireless sensor nodes; and radio frequency (RF) circuitry to transmit communications to and receive communications from the plurality of wireless sensor nodes each including a wireless device with RF circuitry to enable bi-directional communications with the RF circuitry of the apparatus in the wireless network architecture, wherein the one or more processing units of the apparatus are configured to execute instructions to transmit a first communication to a first and a second wireless sensor node each having a known location, and a third wireless sensor nodes having an unknown location, to receive a second communication with an acknowledgement packet from the third wireless sensor node, to determine time difference of arrival information between the apparatus and the first wireless sensor node based on when each of the apparatus and the first wireless nodes receive the acknowledgement packet from the third wireless sensor node, and to determine time difference of arrival information of the reception of the second communication between each of the apparatus and the second wireless sensor node, wherein a transmission time of the first communication being transmitted from the apparatus is used as a time reference for each of the apparatus and the first wireless node.
 11. The apparatus of claim 10, wherein the one or more processing units of the apparatus are configured to execute instructions for a multilateration algorithm to determine a location of the third wireless sensor node using the time difference of arrival information.
 12. The apparatus of claim 10, wherein the apparatus has a first reference clock signal and the first wireless sensor node has a second reference clock signal.
 13. The apparatus of claim 10, wherein the transmitted first communication includes a transmission time of a forward packet that is transmitted to the first, second, and third wireless sensor nodes with the transmission time being used as a time reference for the apparatus, the first wireless sensor node, and the second wireless sensor node.
 14. The apparatus of claim 13, wherein the time difference of arrival information between the apparatus and the first wireless sensor node is determined based on a first time when the apparatus receives an acknowledgement packet from the third wireless sensor node, a second time when the first wireless sensor node receives an acknowledgement packet from the third wireless sensor node, and the time reference.
 15. The apparatus of claim 14, wherein the one or more processing units of the apparatus are configured to execute instructions to determine a difference between the first time and the time reference and also to determine a difference between the second time and the time reference.
 16. An asynchronous system for localization of nodes in a wireless network architecture, comprising: a first, a second, and a third wireless nodes each having known locations and including a wireless device with one or more processing units and RF circuitry for transmitting and receiving communications in the wireless network architecture; and a fourth wireless node having an unknown location and including a wireless device with RF circuitry to enable communications with the first, the second, and the third wireless nodes in the wireless network architecture, wherein the one or more processing units of the first wireless node are configured to execute instructions to receive a first communication with a forward packet from the fourth wireless node, to transmit a second communication to the second, the third, and the fourth wireless nodes in response to the forward packet, and to determine time difference of arrival information of the reception of the first communication between each of the first and the second wireless nodes, wherein a transmission time of the second communication being transmitted from the first wireless node is used as a time reference for each of the first and second wireless nodes.
 17. The system of claim 16, wherein the one or more processing units of the first wireless node are configured to execute instructions for a multilateration algorithm to determine a location of the fourth wireless node using the time difference of arrival information.
 18. The system of claim 16, wherein the first wireless node has a first reference clock signal and the second wireless node has a second reference clock signal.
 19. The system of claim 17, wherein one or more processing units of the fourth wireless node are configured to execute instructions to transmit the first communication including the forward packet to the first, the second, and the third wireless nodes.
 20. The system of claim 19, wherein one or more processing units of the second and the third wireless nodes are configured to execute instructions to receive communications including forward packets from the fourth wireless node and acknowledgement packets from the first wireless node and to record a timestamp and channel sense information for each of the received forward and acknowledgement packets.
 21. The system of claim 20, wherein the time difference of arrival information between the first and the second wireless nodes is determined based on a first time when the first wireless node receives a forward packet from the fourth wireless node, a second time when the second wireless node receives a forward packet from the fourth wireless node, and a time offset between the first and second reference clock signals.
 22. The system of claim 21, wherein the one or more processing units of the first wireless node are configured to execute instructions to determine the time offset between the first and the second reference clock signals based on a third time when the second wireless node receives an acknowledgement packet from the first wireless node, a fourth time when the first wireless node transmits an acknowledgement packet to the second wireless node, and time of flight estimates for communications between the first and the second wireless nodes. 